Make main menu items only show sub menus

I have primary main menu items which are world regions like, USA, Asia etc., I don't want these when clicked on to go anywhere just simply show the drop down menu items and headings and then follow them on to their respective categories etc. How do I stop these main menu headings from going to a page when they are clicked on directly . I want them to only show a drop down menu not move the user off the frontpage or re-load the frontpage.?

This is more Joomla general question. Check this answer:
http://www.ostraining.com/support-forum ... -no-links/